Conventional primer systems for use with sealants, adhesives and coatings generally comprise a large amount of organic solvent plus smaller amounts silane coupling agents and film formers. The solvent based primers provide good adhesion across the substrate-sealant interface and are convenient to use because they dry quickly. Organic solvents are the preferred carriers for such primers since silanes are generally not stable in waterbased systems. However, with the increased environmental concern over the emission of volatile organic compounds (VOC) it is appropriate to eliminate or lower such emissions whenever possible.
U.S. Pat. No. 4,309,326 discloses an aqueous polyester size emulsion for glass fiber comprising an unsaturated water-emulsifiable, silylated polyester resin, an EVA copolymer, and a copolymer of vinyl acetate and a prehydrolyzed, water soluble organosilane.
U.S. Pat. No. 4,394,418 discloses an aqueous sizing composition of a silylated polyvinyl acetate latex containing a low level of silane copolymerized with the vinyl acetate, a water soluble silane, non-ionic surfactants, a polyethylene-containing polymer, a glass fiber lubricant, a hydrocarbon acid and water. The monomeric silanes used in this patent are epoxysilanes and aminosilanes and can be mixed with acrylate containing water soluble silanes. The shelf life of these compositions, however, is generally less than 72 hours.
U.S. Pat. No. 5,393,330 describes emulsions of unsubstituted or halogenated alkyltrialkoxysilanes used as waterproofing agents.
U.S. Pat. No. 4,778,624 discloses a method for the preparation of a stable aqueous emulsion of a poly(silsesquioxane) from substituted and unsubstituted alkylsilanes.
Silane technology for aqueous primers has been developed in the last few years. Most of these developments are based on aminosilanes which uniquely are water soluble, forming water stable hydrolysates. Among these methods, U.S. Pat. No. 5,363,994 teaches the use of aminosilane up to 0.5 parts in combination with a hydrophobic silane in water as a primer. To inhibit condensation of the non-amino silane coupling agents the aqueous primer are required to have a pH from about 2.0 to about 5.5.
WO 9715700 describes a pre-hydrolyzed aminosilane in a concentrated phosphoric acid aqueous solution for use as a primer or conversion treatment on a metallic substrate. However, due to the inherent instability of silane in water, these aqueous primers have shelf lives less than 6 months.
U.S. Pat. No. 5,393,330 describes the use of silane emulsions for hydrophobizing concrete surfaces.
U.S. Pat. Nos. 5,686,523 and 5,714,532, incorporated herein by reference, describe a series of alkoxysilanes which can be formulated into stable emulsion for waterborne coating or sealant formulations as crosslinkers or adhesion promoters. In this technology the silanes are used as additives to a resin system or are incorporated into the resin during resin synthesis.
U.S. Pat. No. 4,689,085 describes the use of bis silyl alkanes in primer formulations but not in emulsions.